The present invention relates to a molded article whose impact resistance is superior, and which comprises a hard part whose rigidity and toughness are superior, and a soft part whose softness and feel are superior, and a process for efficiently producing the molded article.
As to parts such as those for car interior or exterior designs and those for light electric industries, there are known parts which are formed using a hard resin that is superior in its rigidity and toughness. In order to improve their impact resistance and feel, there are also known parts of a molded article formed from one part of the hard resin mentioned above and the other part of a soft elastomer that is superior in its softness and feel, which layers are bonded with each other with the aid of an adhesive agent.
However, such a process for producing the molded article by bonding both parts with the aid of an adhesive agent leaves problems such that a bonding operation using the adhesive agent is markedly complicated and therefore disadvantageous from a viewpoint of production efficiency. Particularly when one part having a concave portion and the other part having a convex portion are inlaid with each other to produce a molded article, such an inlaying operation is remarkably troublesome.
In order to solve the problems mentioned above, for example, JP 48-62875-A and JP 48-62876-A propose a process for producing a molded article, wherein an olefin resin such as polypropylene is injection-molded on a part of a vulcanized olefin rubber such as EPDM, thereby simultaneously performing formation of a part of the olefin resin and heat-melt adhesion between the resulting part of the olefin resin and the part of the olefin rubber.
Each of the references referred to above is incorporated herein by reference in its entirety.
However, the process proposed leaves problems such that the molded articles obtainable by the process are limited in their varieties, because it is substantially impossible to vulcanize a portion of a part composed of an unvulcanized olefin rubber at a post-step, and therefore it is very difficult to carry out a process contrary to the process proposed, that is, a process comprising injection-molding an olefin rubber on a part of an olefin resin and then vulcanizing a portion of the unvulcanized olefin rubber part formed above at a post-step.
Accordingly, it is an object of the present invention to provide a molded article whose impact resistance is superior, and which comprises a hard part whose rigidity and toughness are superior, and a soft part whose softness and feel are superior.
Another object of the present invention is to provide a process for efficiently producing the molded article mentioned above.
The present inventors have undertaken extensive studies to develop a molded article and a production process thereof, which can answer the objects mentioned above. As a result, it has been found that a desired molded article can be efficiently produced by using a specific propylene based block copolymer as the soft part, and thereby the present invention has been obtained.
The present invention provides a molded article comprising:
(i) a part containing a hard synthetic resin; and
(ii) a part containing a soft propylene based block copolymer;
wherein the both parts are integrated with each other, and the soft propylene based block copolymer is prepared by a process comprising the steps of:
(I) carrying out copolymerization of propylene with ethylene until a content of a component(A) which is a propylene-ethylene copolymer component having a content of a repeating unit derived from ethylene of from about 1.5 to 6.0% by weight reaches from about 40 to 85% by weight based on the total weight of the component(A) and a below-defined component(B); and
(II) carrying out copolymerization of propylene with ethylene in the presence of the component (A) prepared in step (I) until a content of the component(B), which is a propylene-ethylene copolymer component having a content of a repeating unit derived from ethylene of from about 7 to 17% by weight, reaches from about 15 to 60% by weight based on the total weight of the components (A) and (B);
provided that an intrinsic viscosity, [xcex7]B, of the component(B) is from about 2 to 5 dl/g, and a ratio of [xcex7]B to an intrinsic viscosity, [xcex7]A, of the component(A), [xcex7]B/[xcex7]A , is from about 0.5 to 1.8.
The present invention also provides a process for producing a molded article, which comprises the steps of:
(1) arranging a part containing a hard synthetic resin in a mold cavity;
(2) injecting a soft propylene based block copolymer melted under heating into said mold cavity; and
(3) cooling the resulting article to be solidified; whereby the molded article formed by integrating the hard synthetic resin part with the soft propylene based block copolymer part is produced; and
wherein the soft propylene based block copolymer is prepared by the same process as mentioned above.
The present invention further provides a process for producing a molded article, which comprises the steps of:
(1) arranging a part containing a soft propylene based block copolymer in a mold cavity;
(2) injecting a hard synthetic resin melted under heating into said mold cavity; and
(3) cooling the resulting article to be solidified; whereby the molded article formed by integrating the hard synthetic resin part with the soft propylene based block copolymer part is produced; and
wherein the soft propylene based block copolymer is prepared by the same process as mentioned above.
The present invention still further provides a process for producing a molded article, which comprises the steps of:
(1) injecting a hard synthetic resin melted under heating and a soft propylene based block copolymer melted under heating independently of each other into a mold having a single cavity through respective cylinders of an injection-molding machine having two or more cylinders; and
(2) cooling the resulting article to be solidified, whereby the molded article formed by integrating the hard synthetic resin part with the soft propylene based block copolymer part is produced; and
wherein the soft propylene based block copolymer is prepared by the same process as mentioned above.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.